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Ligand—Receptor Interactions as Controlled by Wild‐Type and Mutant Thr 370 Lys α 2B ‐Adrenoceptor—G α15 Fusion Proteins
Author(s) -
Pauwels P. J.,
Tardif S.,
Finana F.,
Wurch T.,
Colpaert F. C.
Publication year - 2000
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2000.0740375.x
Subject(s) - oxymetazoline , idazoxan , mutant , chemistry , ligand (biochemistry) , receptor , fusion protein , intrinsic activity , agonist , wild type , g protein , partial agonist , microbiology and biotechnology , biochemistry , antagonist , biology , recombinant dna , prazosin , gene
Fusion proteins were constructed between either a wild‐type or mutant Thr 370 Lys α 2B ‐adrenoceptor (α 2B AR) and a mouse G α15 protein to analyze ligand‐receptor interactions at a receptor/G α15 protein density ratio of 1. Activation of the wild‐type α 2B AR‐G α15 fusion protein in CHO‐K1 cells by (‐)‐adrenaline induced a time‐ and concentration‐dependent (pEC 50 = 7.37 ± 0.13) increase in the intracellular Ca 2+ concentration, which could be antagonized by RX 811059 ( pK B = 7.55 ± 0.15). Whereas d ‐medetomidine and oxymetazoline were as efficacious agonists as (‐)‐adrenaline, the following ligands displayed partial agonist properties: BRL 44408 < atipamezole < clonidine < UK 14304 < BHT 920. A comparison with the mutant Thr 370 Lys α 2B AR‐G α15 fusion protein displayed similar Ca 2+ kinetics and a ligand‐mediated receptor activation profile characterized by higher potencies and greater maximal Ca 2+ responses for the ligands being investigated, including the putative antagonists dexefaroxan and idazoxan. RX 811059 and RX 821002 remained silent. Similar conclusions could be made on enhancement of the ligands’ intrinsic activities by coexpression of the mutant Thr 370 Lys α 2B AR with either a G α15 or G αO Cys 351 Ile protein. The Thr 370 Lys α 2B AR‐G α protein interactions may modify the tertiary structure of the mutant receptor in such a way that some putative α 2 AR antagonists are capable of stabilizing an active receptor conformation, thereby generating positive efficacy.